The Section on Functional Neuroanatomy combines molecular and neuroanatomical methods to characterize and localize dynamic CNS events that relate to issues of mental health and drug abuse. Mapping drug and neurotransmitter receptors using in vitro ligand binding and autoradiography has provided important basic information about brain organization and function. In situ hybridization histochemistry is used to localize and quantify mRNA expression of neuropeptides, monoamine transporters and synthesizing enzymes, adrenal steroid receptors and immediate-early genes in studies of adaptive changes to behavioral, pharmacological, or surgical interventions. (l) The cannabinoid receptor has been localized to specific neuronal elements in brain, and we showed its down regulation in rats after repeated delta-9- tetrahydrocannabinol (THC) administration, which produces behavioral tolerance. 2) In brains of human cocaine addicts, we showed molecular alterations in the basal ganglia caused by chronic cocaine use in an attempt to understand the neurochemical basis of craving and addiction. 3) Studies based on animal models of depression are designed to elucidate brain mechanisms involved in the therapeutic amelioration of chronic stress. Treatments such as antidepressant drug administration and electroconvulsive shock are used in conjunction with acute and chronic stress. Brain systems responsive to both stress and therapeutic treatment include the corticotropin-releasing hormone. (CRH) component of the hypothalamic paraventricular nucleus, which controls the hypothalamic-pituitary-adrenal axis and the noradrenergic locus coeruleus, which plays a crucial role in arousal and vigilance.